Form-relieved face mill cutters have been used for many years in processes for producing gears, particularly spiral bevel and hypoid gears and the like.
Face mill cutters of the form-relieved type comprise a plurality of cutting blades extending in an axial direction from one side of a cutter head with the cutting blades usually arranged and spaced equidistantly about the cutter head. The cutter head itself is adapted to be secured to the rotary cutter spindle carried by a machine tool. Each cutting blade includes a front face and a cutting edge formed by the intersection of the front face with the top, radius, and one side surface of the cutting blade. Wedges and/or shims are commonly utilized in order to correctly orient each cutting blade with respect to the axis of rotation of the cutter head. An example of a form-relieved face mill cutter utilizing shims and wedges is disclosed by U.S. Pat. No. 2,390,112 to Thomas.
The cutting blades which are usually releasably secured to the cutter head may be blades known as outside blades which cut the concave side of the teeth of a work gear, or, the blades may be those known as inside blades which cut the convex side of the work gear teeth. Examples of face mill cutters having outside blades and face mill cutters having inside blades are shown in U.S. Pat. No. 3,192,604 to Whitmore. Alternatively, cutting blades and cutter heads may be of unitary construction, formed from a solid body of material such as high speed steel.
Another type of face mill cutter is shown by U.S. Pat. No. 3,268,980 to Blakesley et al. wherein cutters for roughing and cutters for finishing are shown in which both outside and inside cutting blades are alternatively arranged about a cutter head. This type of cutter forms the entire tooth slot between adjacent teeth on a work gear since each pair of inside and outside blades forms the opposite sides of adjacent teeth.
As with any cutter, continued use of form-relieved face mill cutters causes the cutting blades to become dull and therefore they must be periodically sharpened. It therefore becomes necessary to sharpen each blade by removing an amount of stock material from the front face of each blade thus removing the worn cutting edge and forming a new sharpened edge at the intersection of the newly formed front face and the top, radius, and one side surface of the blade. The side and end faces on the cutting blades used in form-relieved face mill cutters are helicoids. When the front face surface is removed for sharpening purposes, the new front face profile has the same shape and radial position relative to the cutter axis as the prior profile; but, it is displaced axially toward the back of the cutter. When dealing with a set of blades mounted in a cutter head, they must all be equally spaced and the sharpening planes must all have equal spacing. If, for some reason, an extra amount of material were to be removed from the front face of a single blade, the cutting edge would appear to move radially relative to the cutting edges of the other blades. For example, the cutting edge on an outside blade would move inwardly and the cutting edge on an inside blade would move outwardly.
Not only do cutting blades become worn during the cutting process, they are also subjected to intense cutting forces which can cause the blades to be moved from their precise mounted positions on the cutter head. In cutting, it is very important that the cutting edges of the blades track one another within a very narrow range. In generating processes, this range should be about 0.001-0.002 inches (0.0254-0.0508 mm) for rough cutting gear tooth spaces and about 0.0001-0.0003 inches (0.00254-0.00762 mm) for finish cutting. It has commonly been the procedure to reposition each blade after sharpening in order to restore the blade to its proper position. This procedure is known as truing and angling.
Truing is the process wherein each blade is aligned such that the cutting edges thereof are located at the same radial position relative to the axis of the cutter within a narrow tolerance. In the generating process, any blade-to-blade variation will cause the tooth surface to have a flatty appearance.
Angling is the procedure whereby the cutting edge of each blade is positioned at the same angular direction. When optimum tooth surface conditions are required, it has been customary that both angling and truing be controlled by the use of various wedges to adjust the radial and angular positions of each blade. Such cutters are expensive to manufacture, involve a great deal of skill and the amount of time required to make necessary blade adjustments can be quite lengthy, on the order of 2-6 hours for example.
It is an object of the present invention to essentially eliminate the great lengths of time heretofore needed to accomplish truing and angling of blades of a form-relieved face mill cutter.
It is another object of the present invention to incorporate truing and angling of blades as a part of the sharpening process for form-relieved face mill cutters.